Display method and device using photonic crystal characteristics

ABSTRACT

A display method and device using photonic crystal characteristics are disclosed. In the display method using photonic crystal characteristics in accordance with the present invention, when a plurality of particles having electric charges are dispersed in a solvent, an electric field is applied to control inter-particle distance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application Nos.10-2009-0067040 and 10-2010-0022075, filed on Jul. 22, 2009 and Mar. 12,2010, respectively, in the Korean Intellectual Property Office, thedisclosures of which are incorporated herein in their entirety byreference.

FIELD OF THE INVENTION

The present invention relates to a display method and device usingphotonic crystal characteristics. More particularly, the presentinvention relates to a display method and device using photonic crystalcharacteristics, in which, when a plurality of particles having electriccharges are dispersed in a solvent having electrical polarizationcharacteristics, or particles having electric charges and electricalpolarization characteristics are dispersed in a solvent, an electricfield is applied to control inter-particle distances of the particlesand thus control the wavelength of light reflected from the particles.

BACKGROUND OF THE INVENTION

Recently, as the research and development of next-generation displays isactively being pursued, a variety of display means is being introduced.A typical example of the next-generation displays may include anelectronic ink. The electronic ink is a display in which an electricfield is applied to particles of specific colors (e.g., black and white)respectively having negative charges and positive charges to display thespecific colors. Electronic ink has the advantages of low powerconsumption and flexible display. However, the electronic ink is limitedbecause it is difficult to represent various colors since the color ofthe particles is set to specific colors. Electronic ink has the furtherlimitation of being unsuitable for displaying moving images because thedisplay switching speed is low.

To fundamentally overcome the aforementioned problems of theconventional next-generation display, various methods have beensuggested such as a method using the principle of photonic crystal.

The term “photonic crystal” refers to a material or crystal that isrendered in a color corresponding to a specific range of wavelengths byreflecting only light of a particular wavelength range among lightsincident on a regularly arranged microstructure and transmitting lightof the other wavelength ranges. Typical examples of photonic crystalsinclude butterfly wings, beetle shells, etc. Although they do notcontain any pigment, they include a unique photonic crystal structure,so they can produce unique colors.

While photonic crystals existing in nature reflect only light of aparticular wavelength, artificially synthesized photonic crystals canarbitrarily change the crystalline structure thereof (e.g., interlayerthickness of the photonic crystals) by various external stimuli. As aresult, the wavelength range of reflected light can be freely adjustedto cover ultraviolet or infrared regions as well as visible lightregions.

Focusing on this point, the present applicants have arrived at thepresent invention upon discovering that it is possible to implement adisplay method and display device using photonic crystalcharacteristics. An electric field is applied to particles havingelectric charges or electrical polarization characteristics and/or asolvent with electrical polarization characteristics to controlinter-particle distances of the particles and thereby reflect light of acertain wavelength range from the particles.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a display method anddisplay device using photonic crystal characteristics, in which, whenparticles having electric charges are dispersed in a solvent, particleshaving electric charges and electrical polarization characteristics aredispersed in a solvent, or particles having electric charges aredispersed in a solvent having electrical polarization characteristics,an electric field is applied to control inter-particle distances of theparticles. Thus, the wavelength of light reflected from the particles iscontrolled.

Another object of the present invention is to provide a display methodand display device using photonic crystal characteristics, which cancontrol the wavelength of light reflected from particles by adjustingthe intensity, direction, and duration of the application of an electricfield applied to particles and a solvent.

Still another object of the present invention is to provide a displaymethod and display device using photonic crystal characteristics, whichcan independently control inter-particle distances by using a structuresuch as capsules, cells, partitioned electrodes, etc.

In accordance with one aspect of the present invention, there isprovided a display method using photonic crystal characteristics,wherein, when a plurality of particles having electric charges aredispersed in a solvent, an electric field is applied to controlinter-particle distances of the particles.

At least one of the particles and the solvent may have electricalpolarization characteristics.

As the electric field is applied, the inter-particle distance may bemaintained within a specific range by interaction between an electricforce, generated between the electrical field and the particles, causingelectrophoresis of the particles and an electric force generated betweenthe plurality of particles having the electric charges, and as theinter-particle distance are maintained within the specific range, lightof a specific wavelength pattern may be reflected from the plurality ofparticles.

As the electric field is applied, the inter-particle distances may bemaintained within a specific range by interaction between an electricforce generated between the electrical field and the particles causingelectrophoresis of the particles, an electric force generated betweenthe plurality of particles having the electric charges, and an electricforce generated by the electrical polarization, and as theinter-particle distances are maintained within the specific range, lightof a specific wavelength pattern may be reflected from the plurality ofparticles.

The inter-particle distances may vary with changes in at least one ofthe intensity, direction, duration of application, period ofapplication, and number of times of application of the electric field.The wavelength of the light reflected from the particles may vary withchanges in the inter-particle distances.

The difference in refractive index between the particles and the solventmay be more than 0.3.

The particles and the solvent may be encapsulated or partitioned with alight transmissive insulating material.

A region to which the electric field is applied may be divided into atleast two partial regions, and the electric field may be respectivelyapplied to each of the divided partial regions.

After applying the electric field to the particles or the solvent,electric field having the opposite polarity to the applied electricfield may be applied to reset the inter-particle distances.

Before applying the electric filed, a standby electric field may beapplied in order to maintain the inter-particle distances atpredetermined inter-particle distances.

Electric energy may be generated using light passing through theparticles, and the electric field may be applied using the electricenergy.

By applying the electric field through an upper electrode and a lowerelectrode and by setting the intensity of the electric field to be lessthan a predetermined value to control the moving range of the particlesto be less than a predetermined value, a unique color of the particles,the solvent, the upper electrode, or the lower electrode may bedisplayed.

By applying the electric field through an upper electrode and a lowerelectrode and by setting the intensity of the electric field to be equalto or greater than a predetermined value to move the particles toward atleast a partial region of either the upper electrode or the lowerelectrode, a unique color of the particles, the solvent, the upperelectrode, or the lower electrode may be displayed.

By applying an electric field in a state where first particles havingnegative charges and second particles having positive charges aredispersed in the solvent the inter-particle distances between the firstparticles and the inter-particle distances between the second particlesmay be controlled independently from each other by the electric field.

The particles and the solvent may include a material that transmitsvisible light, and as the wavelength range of light reflected from theplurality of particles is out of the wavelength range of visible light,the particles and the solvent may become transparent.

The particles or the solvent may include a material which iselectrically polarized by any one of electronic polarization, ionicpolarization, interfacial polarization, or rotational polarization.

The particles or the solvent may include a superparaelectric orferroelectric material.

The solvent may include a material having a polarity index of 1 orgreater.

The solvent may be made of a material of a gel state.

In accordance with another aspect of the present invention, there isprovided a display device using photonic crystal characteristics,including: a display unit including a plurality of particles havingelectric charges and a solvent containing the particles dispersedtherein; and an electric field generating and/or applying unit forgenerating an electric field applied to the display unit, wherein, whenthe plurality of particles having electric charges are dispersed in thesolvent, the electric field is applied to control inter-particledistances of the particles.

At least one of the particles and the solvent may have electricalpolarization characteristics.

A region to which the electric field is applied may be divided into atleast two partial regions, and the electric field may be respectivelyapplied to each of the divided partial regions.

An electric energy may be generated using light passing through theparticles, and the electric field may be applied using the electricenergy.

By applying the electric field through an upper electrode and a lowerelectrode, and setting the intensity of the electric field to be lessthan a predetermined value to control the moving range of the particlesto be less than a predetermined value, a unique color of the particles,the solvent, the upper or lower electrode may be displayed.

By applying the electric field through an upper electrode and a lowerelectrode, and setting the intensity of the electric field to be equalto or greater than a predetermined value to move the particles to apartial region of either the upper electrode or the lower electrode, anunique color of the particles, the solvent, the upper or lower electrodemay be displayed.

By applying an electric field in a state where first particles havingnegative charges and second particles having positive charges aredispersed in the solvent the inter-particle distances between the firstparticles and the inter-particle distances between the second particlesmay be controlled independently from each other by the electric field.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of the preferredembodiments, given in conjunction with the accompanying drawings, inwhich:

FIGS. 1 and 2 are views illustrating the configuration of particlescontained in a display device in accordance with one embodiment of thepresent invention;

FIG. 3 is a view illustrating the configuration of polarization ofparticles or solvent upon application of an electric field in accordancewith one embodiment of the present invention;

FIG. 4 is a view illustrating unit polarization characteristicsexhibited by the asymmetrical arrangement of molecule in accordance withone embodiment of the present invention;

FIG. 5 is a view showing hysteresis curves of a paraelectric material, aferroelectric material, and a superparaelectric material;

FIG. 6 is a view illustrating a material having a perovskite structurethat may be included in the particles in accordance with one embodimentof the present invention;

FIG. 7 is a view conceptually showing a configuration of control ofinter-particle distances in accordance with a first embodiment of thepresent invention;

FIG. 8 is a view conceptually showing a configuration of control ofinter-particle distances in accordance with a second embodiment of thepresent invention;

FIG. 9 is a view illustrating the configuration of a display device inaccordance with one embodiment of the present invention;

FIGS. 10 and 11 are views conceptually showing the configuration of thedisplay device in accordance with the first and second embodiments ofthe present invention;

FIG. 12 is a view illustrating the configuration of a display deviceincluding an electric field generating and/or applying unit including aplurality of electrodes in accordance with one embodiment of the presentinvention;

FIG. 13 is a view illustrating a configuration in which the particlesand solvent included in the display device are encapsulated in aplurality of capsules in accordance with one embodiment of the presentinvention;

FIG. 14 is a view illustrating a configuration in which the particlesand solvent included in the display device are dispersed in a medium inaccordance with one embodiment of the present invention;

FIGS. 15 and 16 are views illustrating the composition of the particlesand solvent dispersed in a medium in accordance with one embodiment ofthe present invention;

FIG. 17 is a view illustrating a configuration in which the particlesand solvent included in the display device are partitioned into aplurality of cells in accordance with one embodiment of the presentinvention;

FIGS. 18 to 20 are views illustrating a pattern of voltages applied tothe display device in accordance with one embodiment of the presentinvention;

FIG. 21 is a view illustrating the configuration of a display deviceincluding a solar cell unit in accordance with one embodiment of thepresent invention;

FIGS. 22 to 24 are views illustrating a configuration in which theelectrodes constituting the electric field generating and/or applyingunit are patterned in accordance with one embodiment of the presentinvention;

FIG. 25 is a view illustrating the configuration of a display device fordisplaying black or white in accordance with one embodiment of thepresent invention;

FIG. 26 is a view illustrating the configuration of a display device forachieving a transparent display in accordance with one embodiment of thepresent invention;

FIG. 27 is a view illustrating the configuration of a display device forrealizing a photonic crystal display using particles having differentelectric charges from each other in accordance with one embodiment ofthe present invention;

FIG. 28 is a view illustrating the configuration of a display device forrealizing a dual-sided photonic crystal display using an electrode forapplying a ground voltage in accordance with one embodiment of thepresent invention;

FIG. 29 is a view illustrating the configuration of a display device inaccordance with another embodiment of the present invention;

FIGS. 30 and 31 are graphs and photographs showing light reflected fromthe particles as a result of performing an experiment for theapplication of an electric field when the particles having electriccharges are dispersed in a solvent having electrical polarizationcharacteristics in accordance with one embodiment of the presentinvention;

FIGS. 32 and 33 are graphs showing the wavelength of light reflectedfrom the particles as a result of performing an experiment for theapplication of an electric field when the particles having electriccharges are dispersed in various solvents having different polarityindices in accordance with one embodiment of the present invention;

FIGS. 34 and 35 are graphs and photographs showing light reflected fromthe particles as a result of performing an experiment for theapplication of an electric field when the particles having electriccharges and electrical polarization characteristics are dispersed in asolvent in accordance with one embodiment of the present invention;

FIG. 36 is a view showing experimental results for the configuration forrealizing a transparent display in accordance with one embodiment of thepresent invention;

FIG. 37 is a view showing a result of an experiment of the performanceof a display varying with the view angle of the display device (i.e., anexperimental result for the viewing angle of a display) in accordancewith one embodiment of the present invention; and

FIGS. 38 and 39 are views showing results of actually realizing adisplay by applying an electric field and a magnetic field to particleshaving electric charges and magnetism in accordance with still anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different from one another, arenot necessarily mutually exclusive.

For example, a particular feature, structure, and characteristicdescribed herein in connection with one embodiment may be implementedwithin other embodiments without departing from the spirit and scope ofthe present invention. Also, it is to be understood that the positionsor arrangements of individual elements in the embodiment may be changedwithout separating the spirit and scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the invention is defined only by theappended claims that should be appropriately interpreted along with thefull range of equivalents to which the claims are entitled. In thedrawings, like reference numerals identify identical or like elements orfunctions through the several views.

Hereinafter, the configuration of the present invention will bedescribed in detail with reference to the accompanying drawings so thatthose skilled in the art can easily carry out the present invention.

Configuration of Display Device

A main technical feature of a display device in accordance with oneembodiment of the present invention is that when particles havingelectric charges are dispersed in a solvent, particles having electriccharges are dispersed in a solvent having electrical polarizationcharacteristics, or particles having electric charges and electricalpolarization characteristics are dispersed in a solvent, an electricfield is applied to control inter-particle distances of the particlesand thereby implement a full spectrum display using photonic crystalcharacteristics.

[Particles Having Electric Charges]

FIGS. 1 and 2 are views illustrating the configuration of particlescontained in a display device in accordance with one embodiment of thepresent invention.

First, referring to FIG. 1, particles 110 in accordance with oneembodiment of the present invention are dispersed in a solvent 120 asparticles having negative charges or positive charges. At this point,the particles 110 may be arranged at predetermined spaces from eachother by the repulsive force between them caused by electric charges ofthe same polarity. The diameter of the particles 110 may range fromseveral nm to several hundred μm, but the particle diameter is notnecessarily limited thereto.

Referring to FIG. 2, the particles 110 in accordance with one embodimentof the present invention may have a core-shell 112 configuration madefrom different types of materials as shown in (a) of FIG. 2, amulti-core 114 configuration made from different kinds of materials asshown in (b) of FIG. 2, or a cluster structure 116 made from a pluralityof nano-particles as shown in (c) of FIG. 2, in which a charge layer 118having electric charges encloses the particles.

More specifically, the particles 110 in accordance with one embodimentof the present invention may be made of elements, such as silicon (Si),titanium (Ti), barium (Ba), strontium (Sr), iron (Fe), nickel (Ni),cobalt (Co), lead (Pb), aluminum (Al), copper (Cu), silver (Ag), gold(Au), tungsten (W), molybdenum (Mo), or a compound thereof. Also, theparticles in accordance with one embodiment of the present invention maybe made of polymer materials such as PS (polystyrene), PE(polyethylene), PP (polypropylene), PVC (polyvinyl chloride), and PET(polyethylene terephthalate). In addition, the particles in accordancewith one embodiment of the present invention may be made by coatingparticles or a cluster having no electric charge with a material havingelectric charges. Examples of these particles may include particleswhose surfaces are processed (or coated) with an organic compound havinga hydrocarbon group; particles whose surfaces are processed (or coated)with an organic compound having a carboxylic acid group, an ester group,and an acyl group; particles whose surfaces are processed (or coated)with a complex compound containing halogen (F, Cl, Br, I, etc.)elements; particles whose surfaces are processed (coated) with acoordination compound containing amine, thiol, and phosphine; andparticles having electric charges generated by forming radicals on thesurfaces.

Meanwhile, in accordance with one embodiment of the present invention,in order to effectively exhibit photonic crystal characteristics bymaintaining a stable colloidal state without precipitation of theparticles in a solvent, the value of the electrokinetic potential (i.e.,zeta potential) of a colloidal solution comprising particles and asolvent may be greater than or equal to a preset value, the differencein specific gravity between the particles and the solvent may be lessthan or equal to a preset value, and the difference in refractive indexbetween the solvent and the particles may be greater than or equal to apreset value. For instance, the absolute value of the electrokineticpotential of the colloidal solution may be more than or equal to 10 mV,the difference in specific gravity between the particles and the solventmay be less than or equal to 5, and the difference in refractive indexbetween the particles and the solvent may be more than or equal to 0.3.

[Electrical Polarization Characteristics]

Further, in accordance with one embodiment of the present invention, theparticles and/or solvent contained in the display device may haveelectrical polarization characteristics. Such particles and/or solventmay include a material which is electrically polarized with any one ofelectronic polarization, ionic polarization, interfacial polarization,or rotational polarization due to asymmetrical charge distribution ofatoms or molecules as an external electric field is applied.

FIG. 3 is a view illustrating the configuration of polarization ofparticles or solvent upon application of an electric field in accordancewith one embodiment of the present invention.

Referring to (a) and (b) of FIG. 3, if no external electric field isapplied, the particles and/or solvent maintain an electrical equilibriumstate. Whereas, if an external electric field is applied, electriccharges in the particles and/or solvent move in a predetermineddirection, and therefore the particles or solvent can be electricallypolarized. Referring to (c) and (d) of FIG. 3, if no external electricfield is applied, the particles and/or molecules of the solvent withunit polarization caused by electrically asymmetric components arearranged chaotically or randomly. Whereas, if an external electric fieldis applied, the particles and/or the molecules of the solvent having theunit polarization may be re-arranged in a predetermined direction alongthe direction of the external electric field and, thus, may show overallquite a large polarization value. Meanwhile, in accordance with oneembodiment of the present invention, unit polarization may occur in theasymmetrical arrangement of electrons or ions or the asymmetricalstructure of molecules. When no external electric field is applied, avery small remnant polarization value may be shown as well due to thisunit polarization.

FIG. 4 is a view illustrating unit polarization characteristicsexhibited by asymmetrical arrangement of molecules in accordance withone embodiment of the present invention. More specifically, FIG. 4illustrates the case of water molecules (H₂O). In addition to the watermolecules, trichloroethylene, carbon tetrachloride, di-iso-propyl ether,toluene, methyl-t-bytyl ether, xylene, benzene, diethyl ether,dichloromethane, 1,2-dichloroethane, butyl acetate, iso-propanol,n-butanol, tetrahydrofuran, n-propanol, chloroform, ethyl acetate,2-butanone, dioxane, acetone, methanol, ethanol, acetonitrile, aceticacid, dimethylformamide, dimethyl sulfoxide, propylene carbonate, etc.may be employed as the material constituting the particles or solventbecause they represent the unit polarization characteristics due to theasymmetry of a molecular structure. For reference, the polarity indexused to compare the polarization characteristics of materials is anindex that shows the relative degree of polarization of a given materialwith respect to the polarization characteristics of water (H₂O).

Moreover, the particles or solvent in accordance with one embodiment ofthe present invention may include a ferroelectric material, which showsan increase in polarization upon application of an external electricfield and shows a large remnant polarization and remnant hysteresis evenwithout the application of an external electric field. The particles orsolvent may include a superparaelectric material, which shows anincrease in polarization upon application of an external electric fieldand shows no remnant polarization and no remnant hysteresis when noexternal electric field is applied. Referring to FIG. 5, it can be seenthat there are hysteresis curves which are obtained according to theexternal electric fields of a paraelectric material 510, theferroelectric material 520, and the superparaelectric material 530.

Further, the particles or solvent in accordance with one embodiment ofthe present invention may include a material having a perovskitestructure. Examples of materials having a perovskite structure, such asABO₃, may include materials such as PbZrO₃, PbTiO₃, Pb(Zr,Ti)O₃, SrTiO₃BaTiO₃, (Ba, Sr)TiO₃, CaTiO₃, LiNbO₃, etc.

FIG. 6 is a view illustrating a material having a perovskite structurethat may be included in the particles or solvent in accordance with oneembodiment of the present invention. Referring to FIG. 6, the positionof Zr (or Ti) in PbZrO₃ (or PbTiO₃) (i.e., B in an ABO₃ structure) mayvary with the direction of the external electric field applied to PbZrO₃(or PbTiO₃), and thus, the overall polarity of PbZrO₃ (or PbTiO₃) may bechanged.

Meanwhile, in accordance with one embodiment of the present invention,the solvent may include a material having a polarity index of 1 orgreater.

The composition of the particles and solvent is not necessarily limitedto those listed above, but may be appropriately changed within the scopeof the objects of the present invention, i.e., within the scope in whichthe inter-particle distances of the particles can be controlled by anelectric field.

[Operating Principle and Configuration of Display Device]

Meanwhile, in accordance with a first embodiment of the presentinvention, when a plurality of particles having electric charges of thesame sign or polarity are dispersed in a solvent having electricalpolarization characteristics, if an electric field is applied to thedispersion including the particles and the solvent containing thedispersed particles, electrical attraction proportional to the intensityof the electric field and the charge amount of the particles acts on theparticles due to the electric charges of the particles. Therefore, theplurality of particles moves in a predetermined direction byelectrophoresis, thus narrowing the inter-particle distances. Incontrast, electrical repulsion generated between the particles havingthe electric charges of the same sign or polarity increases as theinter-particle distances become smaller resulting in a predeterminedequilibrium state while preventing the inter-particle distances fromcontinuing to decrease. Further, the solvent is electrically polarizedin a predetermined direction due to the electrical polarizationcharacteristics of the solvent. Thus, electrical attraction is locallygenerated and exerts a predetermined effect upon the inter-particledistances between the particles electrically interacting with thepolarized solvent. That is, in accordance with the first embodiment ofthe present invention, the plurality of particles can be regularlyarranged at distances where electrical attraction induced by an externalelectric field, electrical repulsion between the particles havingelectric charges of the same polarity, electrical attraction induced bypolarization, and the like are in equilibrium. According to the aboveprinciple, the inter-particle distances can be controlled atpredetermined levels, and the particles arranged at predetermineddistances can function as photonic crystals. Since the wavelength oflight reflected from the regularly spaced particles is determined by theinter-particle distance, the wavelength of the light reflected from theparticles can be arbitrarily controlled by controlling theinter-particle distances. Here, a pattern of the wavelength of reflectedlight may be diversely represented by the factors, such as the intensityand direction of the applied electric field, the size and mass of theparticles, the refractive indices of the particles and the solvent, thecharge amount of the particles, the electrical polarizationcharacteristics of the solvent, the concentration of the particlesdispersed in the solvent, etc.

FIG. 7 is a view conceptually showing a configuration of control ofinter-particle distances in accordance with a first embodiment of thepresent invention. Referring to FIG. 7, if no external electric field isapplied, unit polarized solvent 710 near particles 720 having electriccharges can be intensively arranged in the direction of the particles byinteraction with the electric charges of the particles, and the unitpolarized solvent 710 can be arranged more chaotically or randomly asits distance from the charged particles increases (See (a) of FIG. 7).Also, referring to FIG. 7, if an external electric field is applied, theunit polarized solvent 710 located in a region not affected by theparticles 720 (i.e., a region far away from the particles 720) isre-arranged in the direction of the electric field. The unit polarizedsolvent 710 located in a region strongly affected by electricalattraction induced by the electric charges of the particles 720 (i.e., asurrounding region of the particles 720) can be asymmetrically arrangedby interaction between the electrical attraction induced by the electriccharges of the particles 720 and the electrical attraction induced bythe external electric field. As such, the region where the solvent 710in the surrounding region of the particles 720 is asymmetricallyarranged, i.e., a polarization region 730, acts like one large,electrically polarized particle and thus can interact with other largepolarization regions, thereby enabling the particles having electriccharges to be regularly arranged while maintaining a predeterminedinterval or space therebetween (See (b) of FIG. 7).

In accordance with a second embodiment of the present invention, when aplurality of particles having electric charges of the same sign orpolarity as each other and electrical polarization characteristics aredispersed in a solvent, if an electric field is applied to the particlesand the solvent, electrical attraction proportional to the intensity ofthe electric field and the charge amount of the particles acts on theparticles due to the electric charges of the particles. Therefore, theparticles move in a predetermined direction by electrophoresis, thusnarrowing the inter-particle distances. In contrast, electricalrepulsion generated between the particles having the electric charges ofthe same sign or polarity increases as the inter-particle distancesdecreases, thus reaching a predetermined equilibrium state whilepreventing the inter-particle distances from continuing to decrease. Theparticles are electrically polarized in a predetermined direction due tothe electrical polarization characteristics of the particles. Thus,electrical attraction is locally generated between the polarizedparticles and exerts a predetermined effect upon the inter-particledistances.

That is, in accordance with the second embodiment of the presentinvention, the particles can be regularly arranged at a distance whereelectrical attraction induced by an external electric field, electricalrepulsion between the particles having electric charges of the samesign, and electrical attraction induced by polarization are inequilibrium. According to the above principle, the inter-particledistances can be controlled at predetermined intervals, and theplurality of particles arranged at predetermined intervals can functionas photonic crystals. Since the wavelength of light reflected from theplurality of regularly arranged particles is determined by theinter-particle distances, the wavelength of the light reflected from theparticles can be accurately controlled by controlling the inter-particledistances. Here, a pattern of the wavelength of reflected light may bediversely represented by the factors, such as the intensity anddirection of an electric field, the size and mass of the particles, therefractive indices of the particles and the solvent, the charge amountof the particles, the electrical polarization characteristics of theparticles, the concentration of the particles dispersed in the solvent,etc.

FIG. 8 is a view conceptually showing a configuration of control ofinter-particle distances in accordance with a second embodiment of thepresent invention. Referring to FIG. 8, if no external electric field isapplied, particles 810 are not polarized (see (a) of FIG. 8). If anexternal electric field is applied, the particles 810 can beelectrically polarized due to the electrical polarizationcharacteristics of the material in the particles 810. Accordingly, theparticles 810 can be regularly arranged while maintaining apredetermined interval or space therebetween (see (b) of FIG. 8).

In the first and second embodiments of the present invention, thegreater the electrical polarization value of the solvent or particles,the higher the degree of interaction between the polarization regions730 or between the polarized particles 810, thereby enabling theparticles to be more regularly arranged.

FIG. 9 is a view illustrating the configuration of a display device inaccordance with one embodiment of the present invention.

Referring to FIG. 9, a display device 900 in accordance with oneembodiment of the present invention may include a display unit 910 andan electric field generating and/or applying unit 920. Morespecifically, in accordance with the first embodiment of the presentinvention, a plurality of particles 912 having electric charges of thesame sign, which are dispersed in a solvent 914 having electricalpolarization characteristics, may be included in the display unit 910.In accordance with the second embodiment of the present invention, aplurality of particles 912 having electric charges of the same sign andelectrical polarization characteristics which are dispersed in a solvent914 may be included in the display unit 912.

FIGS. 10 and 11 are views conceptually showing the configuration of thedisplay device in accordance with the first and second embodiments ofthe present invention. Since the first and second embodiments of thepresent invention have been already described in full details withreference to FIGS. 7 and 8, additional explanation of FIGS. 10 and 11are omitted.

In accordance with one embodiment of the present invention, the displayunit 910 performs the function of reflecting light of a certainwavelength range (i.e., light of a certain color when viewed from avisible light region) depending on the intensity and/or direction of anapplied electric field. As stated above, this can be achieved bycontrolling the inter-particle distances of the particles 912 dependingon the intensity and/or direction of the electric field applied to thedisplay unit 910.

Next, the electric field generating and/or applying unit 920 performsthe function of applying an electric field of a predetermined intensityand/or direction to the display unit 910. The intensity and/or directionof the electric field applied by the electric field generating and/orapplying unit 920 can be properly controlled over a wavelength range oflight desired to be reflected from the display unit 910.

More specifically, FIG. 12 is a view illustrating the configuration of adisplay device including an electric field generating or applying unitincluding a plurality of electrodes in accordance with one embodiment ofthe present invention.

Referring to FIG. 12, electric field generating and/or applying units1222, 1224, 1226, and 1228 may include electrodes 1222, 1224, 1226, and1228 that are capable of independently applying an electric field onlyto partial regions of a display unit 1210 in order to control theinter-particle distances of the particles 1212 included in the displayunit 1210 more precisely and independently. The electrodes 1222, 1224,1226, and 1228 can be individually controlled by a fine driving circuit,such as a thin film transistor (TFT). The electric field generatingand/or applying units 1222, 1224, 1226, and 1228 may be made of a lighttransmissive material so as not to obstruct the progression of the lightemitted from the display unit 1210. For instance, the electric fieldgenerating and/or applying units 1222, 1224, 1226, and 1228 may be madeof indium tin oxide (ITO), titanium oxide (TiO₂), carbon nano tubes(which are light transmissive materials), and other electricallyconductive polymer films.

Referring to FIG. 12, the electric field generating and/or applyingunits 1222, 1224, 1226, and 1228 may include a first electrode 1222, asecond electrode 1224, a third electrode 1226, and a fourth electrode1228. Because no electric filed is applied to a space covered by thefirst electrode 1222 to which no voltage is applied, the particles 1212located in the space covered by the first electrode 1222 may beirregularly arranged. Therefore, the display unit 1210 controlled by thefirst electrode 1222 may not represent a color caused by photoniccrystal. Next, because electric fields corresponding to respectivevoltages are applied to spaces covered by the second electrode 1224,third electrode 1226, and fourth electrode 1228 to which voltages ofdifferent levels are applied, the particles 1212 located in the spacescovered by these electrodes may be regularly arranged at predeterminedinter-particle distances from each other while electrical attractioncaused by the electric fields (i.e., a force that causeselectrophoresis), electrical repulsion between the particles 1212 havingelectric charges of the same sign, and electrical attraction caused bythe polarization (or its increase) of the particles 1212 or solvent1214, etc. are in equilibrium. Accordingly, the display unit 1210controlled by the second electrode 1224, third electrode 1226, andfourth electrode 1228 can reflect light of different wavelength rangesfor the respective regions (i.e., structural colors caused by photoniccrystals). For instance, under the assumption that a voltage applied tothe fourth electrode 1228 is greater than a voltage applied to the thirdelectrode 1226, the inter-particle distances of the particles 1212located in the space covered by the fourth electrode 1228 may benarrower than the inter-particle distances of the particles 1212 locatedin between the third electrode 1226. Thus, the display unit 1210controlled by the fourth electrode 1228 can reflect light of a shorterwavelength than the display unit 1210 controlled by the third electrode1226 can.

FIG. 13 is a view illustrating a configuration in which the particlesand solvent included in the display device are encapsulated in aplurality of capsules in accordance with one embodiment of the presentinvention.

Referring to FIG. 13, particles 1312 and solvent 1314 included in adisplay unit 1300 encapsulated in capsules 1322, 1324, 1326, and 1328made of a light transmissive material. By encapsulating the particles1312 and the solvent 1314 as shown in FIG. 13, direct interference, suchas incorporation, between the particles 1312 and solvent 1314 includedin different capsules can be prevented; the particles can be preventedfrom being irregularly arranged due to electrohydrodynamic (EHD) motionof the particles having electric charges; the film processability of thedisplay device 1300 can be improved by making sealing of the particlesand the solvent easier; and the inter-particle distances of theparticles contained in the display device 1300 can be independentlycontrolled for each capsule.

Referring to FIG. 13, the display device 1300 may include four capsules1322, 1324, 1326, and 1328. A first voltage, second voltage, thirdvoltage, and fourth voltage can be respectively applied to electrodes1332, 1334, 1336, and 1338 located in the portions of the first capsule1322, second capsule 1324, third capsule 1326, and fourth capsule 1328.Accordingly, the respective capsules, to which electric fields ofdifferent intensities and different directions are applied, reflectlight of different wavelength ranges. As such, with the display device1300 in accordance with one embodiment of the present invention, anindependent display can be implemented for each capsule.

Unlike FIG. 13, if the electrodes and the capsules are not disposed in acorresponding way to each other and instead, a region covered byelectrodes is smaller than a capsule or one capsule is covered by two ormore electrodes, an independent display can be implemented as desiredfor a given region of the display unit by using an electrode pattern.That is, in accordance with one embodiment of the present invention,when an electric field is applied to a specific region in a capsulethrough one of the electrodes that covers the capsule, only the solventand/or particles existing in the specific region among the particlesexisting in the capsule reacts with the electric field, but theparticles and/or solvent existing in other regions does not react withthe electric field. Thus, a region (i.e., display region) on which lightof a specific wavelength is reflected can be determined by an electrodepattern, rather than by the size or pattern of the capsules.

FIG. 14 is a view illustrating a configuration in which the particlesand solvent included in the display device are dispersed in a medium inaccordance with one embodiment of the present invention.

Referring to FIG. 14, the particles and solvent included in a displaydevice 1400 in accordance with one embodiment of the present inventionmay be dispersed in a medium 1430 made of a light transmissive material.More specifically, a predetermined amount of particles and solvent isdispersed and distributed in the form of droplets in the lighttransmissive material 1430 which does not change in response to externalstimuli such as an electric field, thus partially isolating theparticles contained in the display device 1400. That is, in accordancewith one embodiment of the present invention, the solvent with theparticles dispersed therein is dispersed and distributed in the lighttransmissive medium 1430 to prevent the occurrence of directinterference, such as incorporation, between the particles or solventincluded in different regions to thereby control the inter-particledistances of the particles contained in the display device 1400 moreindependently.

The display device 1400 may include a plurality of regions 1412 and 1414included in the medium 1430. More specifically, the inter-particledistances of the particles contained in a first region 1410 located inbetween the first electrodes 1442 to which a first voltage is appliedand the inter-particle distances of the particles contained in thesecond region 1420 located in between second electrodes 1444 to which asecond voltage is applied can be controlled independently from eachother. Therefore, the first region 1410 and the second region 1420 canreflect light of different wavelength ranges. Accordingly, with thedisplay device 1400, an independent display can be implemented for eachregion.

FIG. 15 is a view illustrating the composition of a solutionencapsulated in a light transmissive medium in accordance with oneembodiment of the present invention. For reference, FIG. 15 correspondsto a photograph taken by an electron microscope on a cross-section ofthe display device 1300 mentioned with reference to FIG. 13.

Referring to FIG. 15, it can be seen that the solvent with the particles1510 dispersed therein is encapsulated in a light transmissive materialwhich does not change by an electric field. In accordance with oneembodiment of the present invention, the solution (i.e., mixture of theparticles and the solvent) with the particles 1510 dispersed in thesolvent in a colloidal state is mixed with a different kind ofimmiscible solution to form an emulsion, and then the emulsion interfaceis coated with the light transmissive material 1520, thereby beingencapsulated in the light transmissive material 1520. Here, an oxidizedsteel (FeO_(x)) cluster coated with a charge layer may be used as theparticles, a solvent having electrical polarization characteristics maybe used as the solvent, and a light transmissive polymer materialcontaining gelatin may be used as the capsule material.

FIG. 16 is a view illustrating the composition of the particles andsolvent dispersed in a medium in accordance with one embodiment of thepresent invention. For reference, FIG. 16 corresponds to a photographtaken by an electron microscope on a cross-section of the display device1400 mentioned with reference to FIG. 14.

Referring to FIG. 16, it can be seen that the solvent 1620 with theparticles 1610 dispersed therein is dispersed in a medium 1630 made oflight transmissive material of a solid or gel state which does notchange in response to external stimuli, such as an electric field, amagnetic field, etc. The particles 1610 having electric charges aredispersed in the solvent 1620 and the resultant dispersion are evenlymixed in the light transmissive medium 1630 in the form of droplets,thereby obtaining the composition shown in FIG. 16. Moreover, theparticles 1610 may be an oxidized steel (FeO_(x)) cluster coated with acharge layer, the solvent 1620 may be ethylene glycol (EG), and themedium 1630 may be polydimethylsiloxane (PDMS).

FIG. 17 is a view illustrating a configuration in which the particlesand solvent included in the display device are partitioned into aplurality of cells in accordance with one embodiment of the presentinvention.

Referring to FIG. 17, the particles 1712 and solvent 1714 included inthe display device 1700 can be isolated by partition walls or the likemade of an insulating material and partitioned into cells 1732, 1734,1736, and 1738. By partitioning the particles 1712 and the solvent 1714,direct interference, such as incorporation, between the particles 1712and/or the solvent 1714 to be included in different cells can beprevented from occurring. Accordingly, the inter-particle distances ofthe particles contained in the display device 1700 can be independentlycontrolled for each cell, and the particles can be prevented from beingirregularly arranged due to electrohydrodynamic (EHD) motion of theparticles having electric charges.

Meanwhile, unlike in FIG. 17, even if the electrodes and the cells arenot disposed in a corresponding manner to each other but instead aregion covered by electrodes is smaller than a cell or one cell iscovered by two or more electrodes, an independent display can beimplemented as desired for a given region of the display unit by usingan electrode pattern. That is, when an electric field is applied to aspecific region in a cell through one of the electrodes that covers thecell, only the solvent and/or particles existing in the specific regionamong the particles existing in the cell reacts with the electric field,but the particles and/or solvent existing in other regions does notreact with the electric field. Thus, a region (i.e., display region) onwhich light of a specific wavelength is reflected can be determined byan electrode pattern, rather than by the size or pattern of the cells.

As mentioned above, by encapsulating the particles and the solvent ordispersing them in a medium or partitioning them, the inter-particledistances can be independently controlled for each capsule, each region,or each cell, thereby enabling more precise display and making themaintenance and repair of the display device easier.

Meanwhile, although the embodiments of FIGS. 12 to 17 have beendescribed with respect to the case where both of the upper and lowerelectrodes are divided into a plurality of electrodes, either one of theupper and lower electrodes may be formed as a common electrode. Forinstance, in the actual application to display products, the upperelectrode may be formed as a common electrode made of a transparentelectrode material, while the lower electrode may be divided into unitcells and connected to a transistor for driving each cell and may not bemade of a transparent electrode material.

FIGS. 18 to 20 are views illustrating a pattern of voltages applied tothe display device in accordance with one embodiment of the presentinvention.

First, referring to FIG. 18, the display device in accordance with oneembodiment of the present invention may further include a control unit(not shown) that performs the function of resetting or initializing theinter-particle distances of the particles at times between the intervalsof changing of the intensity and/or direction of an electric field whensequentially applying electric fields of different intensities and/ordifferent directions to the dispersion including the particles and thusachieving a continuous display. More specifically, when sequentiallyapplying a first voltage and a second voltage using the electric fieldgenerating and/or applying unit to the dispersion including theparticles and the solvent, the control unit performs the function ofbringing the inter-particle distances arranged at predetermineddistances by the first voltage back to the initial or reset state byapplying a reset voltage having the opposite polarity to the firstvoltage to the dispersion before applying the second voltage after theapplication of the first voltage. With this, the display device canimprove display performance, including improving the operating speed andsuppressing afterimages. Moreover, the reset voltage is applied with theopposite polarity to the just previously applied voltage. Therefore,even when the display device is turned off, the operating speed can beraised by forcibly moving the particles moved and arranged in apredetermined direction by the just previously applied voltage into theopposite direction.

Next, referring to FIG. 19, the display device in accordance with oneembodiment of the present invention may further include a control unit(not shown) that performs the function of maintaining the inter-particledistances at predetermined distances (stand-by distances) in advancewhen sequentially applying electric fields of different intensities anddifferent directions to the dispersion including the particles and thesolvent and achieving a continuous display. More specifically, whensequentially applying a first voltage and a second voltage using theelectric field generating and/or applying unit to the dispersionincluding the particles and the solvent, the control unit in accordancewith one embodiment of the present invention performs the function ofrapidly adjusting the inter-particle distances to desired inter-particledistances by applying a predetermined standby voltage in advance andthen applying the first voltage or the second voltage. With this, thedisplay device in accordance with one embodiment of the presentinvention can improve display performance, including increasing responsespeed and making screen change faster. That is, in the conventionalelectronic paper technology, particles of a specific color had to bemoved to run through from one end to the opposite end in a cell in orderto display a particular color. Contrastingly, in the present invention,photonic crystals can be realized in a manner that a standby voltagehaving a relatively low level enough not to make reflected light in avisible spectrum appear is applied to form the stand-by inter-particledistances not yet corresponding to the visible light, and then a voltageof a specific level or greater is applied to reflect light in thevisible spectrum. Hence, photonic crystals for reflecting light in thevisible spectrum can be realized just by moving the particles slightly,thereby making the operating speed of such a reflection-type displaydevice faster.

Subsequently, referring to FIG. 20, the display device in accordancewith one embodiment of the present invention may further include acontrol unit (not shown) that performs the function of applying anelectric field of various patterns of the intensity, duration ofapplication, etc. of the electric field when sequentially applyingelectric fields of different intensities and/or different directions tothe dispersion and achieving a continuous display. More specifically,when applying a voltage using the electric field generating and/orapplying unit to the dispersion including the particles and the solvent,the control unit in accordance with one embodiment of the presentinvention can increase or decrease the level of a voltage to apredetermined voltage (see (a) of FIG. 20), can extend or reduce theduration or period of application of a certain voltage (see (b) of FIG.20), and can obtain the same effect as continuous application of avoltage by repeatedly applying a discontinuous pulse voltage (see (c) ofFIG. 20). By doing so, the display device in accordance with oneembodiment of the present invention can improve display performance,including enabling display of various patterns and reducing powerconsumption.

It should be noted, however, that the electric field application patternin accordance with the present invention is not necessarily limited tothose listed above, but may be appropriately changed within the scope ofthe objects of the present invention, i.e., within the scope in whichthe inter-particle distances can be controlled by an electric field.

FIG. 21 is a view illustrating the configuration of a display deviceincluding a solar cell unit in accordance with one embodiment of thepresent invention.

Referring to FIG. 21, a display device 2100 may further include a solarcell unit 2130 that performs the function of generating an electromotiveforce by using light transmitted through the display device 2100 andstoring it. The electromotive force generated by the solar cell unit2130 can be used to generate and apply a voltage using the electricfield generating and/or applying unit 2120, whereby the display device2100 can realize the above-described photonic crystal display withoutdepending on an external power supply. However, a combination of thedisplay device and the solar cell unit in accordance with the presentinvention is not necessarily limited to those listed above, but theelectromotive force generated by the solar cell unit may be used forpurposes other than driving the display device.

FIGS. 22 to 24 are views illustrating a configuration in which theelectrodes constituting the electric field generating and/or applyingunit are patterned in accordance with one embodiment of the presentinvention.

First, referring to FIG. 22, a lattice-shaped insulating layer 2230 canbe formed on the lower electrode 2225 (or upper electrode 2220) of theelectric field generating and/or applying unit, and thus the lowerelectrode 2225 (or upper electrode 2220) can be patterned atpredetermined intervals.

In accordance with the display device shown in FIG. 22, the patterninginterval of the electrodes is set approximately from several μm toseveral hundreds of μm, thereby preventing the particles from beingirregularly arranged due to electrohydrodynamic (EHD) motion of theparticles having electric charges and thus achieving uniform display. Inparticular, in accordance with the display device shown in FIG. 22, theparticles can be effectively prevented from being biased byelectrohydrodynamic motion without passing through a complicatedprocess, such as encapsulation or cell partitioning, which requires alot of time and cost.

Next, referring to FIG. 23, the lower electrode (or upper electrode) ofthe electric field generating and/or applying unit in accordance withone embodiment of the present invention may be divided into twoelectrodes (a first electrode 2320 and a second electrode 2325). Morespecifically, referring to FIG. 24, the first electrode 2420 and secondelectrode 2425 constituting the lower electrode (or upper electrode) ofthe electric field generating and/or applying unit can be patterned inthe form of alternating teeth.

In accordance with the display device shown in FIGS. 23 and 24, it canbe advantageous in terms of cost saving because electrodes can be formedonly on one substrate, and the operating speed of the display device canbe raised because the moving distance of the particles caused byapplication of an electric field is reduced.

It should be noted, however, that an electrode pattern in accordancewith the present invention is not necessarily limited to those listedabove, but may be appropriately changed within the scope of the objectsof the present invention, i.e., within the scope in which theinter-particle distances can be controlled by an electric field.

Meanwhile, as the display device using photonic crystal characteristicsoperates on the principle that light of a specific wavelength amongincident light is selectively reflected, it may not be easy to representfull black or full white by the display device using photonic crystalcharacteristics. The following description will be made about theconfiguration for displaying black or white by the display device usingphotonic crystal characteristics.

FIG. 25 is a view illustrating the configuration of a display device fordisplaying black or white in accordance with one embodiment of thepresent invention.

Referring to FIG. 25, a display unit 2510 may include black particles2512, and an electric field generating or applying unit may include atransparent upper electrode 2520 and first and second lower electrodes2522 and 2524 of white. First, if the intensity of an electric fieldapplied to the display unit 2510 is less than a predetermined value orno electric field is applied, the particles 2512 may not form photoniccrystals, but may reflect black, which is their own unique color, orreflect scattered light caused by the difference in refractive indexbetween the particles and the solvent, thereby enabling the display unit2510 to display black (see (a) of FIG. 25). Although not shown in FIG.25, the black particles 2512 can be arranged in close contact with theupper electrode 2520 by applying an electric field above a thresholdvalue to the display unit 2510. In this case, too, the display unit 2510is able to display black. Next, if an electric field of an appropriateintensity is applied to the display unit 2510, light of a certain,desired wavelength range can be reflected from the particles 2512forming photonic crystals (see (b) of FIG. 25). And then, if an electricfield above a predetermined intensity is applied to the display unit2510, the magnitude of electrical attraction that causes electrophoresisbecomes too large, and thus the inter-particle distances 2512 are notmaintained at appropriate distances and the particles 2512 may be drawnto one side. For instance, if an electric field above a predeterminedvalue is applied only to the portion of the first lower electrode 2522,all the particles 2512 included in the display unit 2510 do not formphotonic crystals but may be drawn to a narrow region covered by thefirst lower electrode 2522. Therefore, the second lower electrode 2524can reflect white, which is its own unique color, without being affectedby the black particles 2512, and thus the display unit 2510 can displaywhite (see (c) of FIG. 25).

However, although the embodiment of FIG. 25 has been described withrespect to the case where the colors of the particles and the electrodesare specified to black and white, the present invention is notnecessarily limited thereto but the colors of the particles and theelectrodes applicable to the display device of the present invention canbe changed as desired and, further, can be set to be transparent. Thefollowing description will be made about the configuration for achievinga transparent display by the display device using photonic crystalcharacteristics.

FIG. 26 is a view illustrating the configuration of a display device forachieving a transparent display in accordance with one embodiment of thepresent invention.

Referring to FIG. 26, a display unit 2610 may include transparentparticles 2612 containing a visible light transmitting material, such asSiO_(X), and an electric field generating and/or applying unit mayinclude an upper electrode 2620 and a lower electrode 2622 that are alsotransparent. First, if the intensity of an electric field applied to thedisplay unit 2610 is less than a predetermined value or no electricfield is applied, the particles 2612 may not form photonic crystals andrepresent colors produced by photonic crystals and may scatter incidentlight due to the difference in refractive index between the particlesand the solvent (see (a) of FIG. 26). Next, if an electric field of anappropriate intensity is applied to the display unit 2610, light of acertain, desired wavelength range can be reflected from the particles2612 forming photonic crystals (see (b) of FIG. 26). And then, if anelectric field above a preset intensity is applied to the display unit2610, the magnitude of electrical attraction that causes electrophoresisbecomes too large, and thus the inter-particle distances 2612 canreflect only light of a wavelength range (e.g., ultraviolet spectrum)shorter than the visible spectrum. That is, in this case, light in thevisible spectrum is not reflected by photonic crystals but transmittedso the upper electrode 2620, the lower electrode 2622, and the particles2612 all become transparent, and thus the display device of FIG. 26becomes entirely transparent (see (c) of FIG. 26).

Meanwhile, although not shown concretely in FIG. 26, in (c) of FIG. 26,if an electrode having a specific color is used as the lower electrode,the color of the lower electrode may be displayed because light in thevisible spectrum is not reflected by photonic crystals but transmittedand then reflected with the lower electrode.

That is, in the display device in accordance with the present invention,if a voltage below a specific level is applied, incident light isscattered and becomes translucent or opaque, if a voltage of a specificrange is applied, incident light in the visible spectrum is reflected byregular arrangement (i.e., photonic crystals) of the particles tothereby display a predetermined color, and if a voltage exceeding aspecific level is applied, the inter-particle distances become toonarrow. Hence, incident light in the visible spectrum is transmitted,and incident light in the ultraviolet spectrum having a wavelength rangeshorter than the visible spectrum is reflected and becomes transparent.Therefore, according to the display device in accordance with thepresent invention, it is possible to make the color changing glass orthe like where not only the light of a certain wavelength range can bereflected, but also it may become transparent or opaque. Further, it ispossible to implement a display system, which makes a specific color orpattern, present on one side with respect to the display device,visible, or invisible to an observer placed at the other side byadjusting the transparency of the display device.

FIG. 27 is a view illustrating the configuration of a display device forrealizing a photonic crystal display using particles having differentelectric charges in accordance with one embodiment of the presentinvention.

First, referring to FIG. 27, a display unit 2710 of a display device2700 may include particles having different electric charges, i.e., onetype of particles 2712 having negative charges and the other type ofparticles 2714 having positive charges. As an electric field is appliedto the display unit 2710, the particles 2712 having negative charges,and the particles 2714 having positive charges may be respectively movedin the opposite direction and regularly arranged. For instance, if anupper electrode 2720 of the electric field generating and/or applyingunit is a positive electrode and a lower electrode 2725 thereof is anegative electrode, the particles 2712 having negative charges and theparticles 2714 having positive charges may be moved in the upperelectrode 2720 direction and in the lower electrode 2725 direction,respectively, and arranged as photonic crystals while maintainingpredetermined inter-particle distances. In this case, the display device2700 can reflect light of a certain wavelength range against both sides(i.e., the side of the upper electrode 2720 and the side of the lowerelectrode 2725) and thus can realize a double-sided display.Furthermore, if the charge amount of the particles 2712 having negativecharges and the charge amount of the particles 2714 having positivecharges are different from each other, as an electric field is applied,the inter-particle distances of the particles 2712 having negativecharges and the inter-particle distances of the particles 2714 havingpositive charges may differ from each other. Thus, the display device2700 can reflect light of different wavelength ranges against bothsides, and thus can realize a display, both sides of which arecontrolled independently from each other.

Meanwhile, as explained with reference to FIG. 25, the particles 2712having negative charges and particles 2714 having positive charges thatare included in the display device 2700 of FIG. 27 may have their uniquecolors. In this case, different colors can be displayed on the upper andlower parts of the display device just by adjusting the polarity of anelectric field applied to the upper electrode 2720 and the lowerelectrode 2725. For instance, assuming that the particles 2712 havingnegative charges are in black and the particles 2714 having positivecharges are in white, when a positive voltage is applied to the upperelectrode 2720, the black particles 2712 having negative charges may bemoved toward the upper electrode 2720 to display black on the upper partof the display device. When a negative voltage is applied to the upperelectrode 2720, the white particles 2714 having positive charges may bemoved toward the upper electrode 2720 to display white on the upper partof the display device. In line with this, the particles 2712 havingnegative charges and the particles 2714 having positive charges may alsoform photonic crystals to thereby reflect light of a certain wavelength.Thus, white and black can be displayed on the same cell, and reflectedlight of a certain wavelength range can be displayed as well.

FIG. 28 is a view illustrating the configuration of a display device forrealizing a dual-sided photonic crystal display using an electrode forapplying a ground voltage in accordance with one embodiment of thepresent invention.

Referring to FIG. 28, a display device 2800 may include a groundelectrode 2830 for applying a ground voltage between an upper electrode2820 and a lower electrode 2825. As different voltages are applied tothe upper electrode 2820 and the lower electrode 2825 respectively,electric fields having different directions and magnitudes can beindependently applied to a space between the upper electrode 2820 andthe ground electrode 2830 and a space between the lower electrode 2825and the ground electrode 2830, respectively. Therefore, particlespresent in a first display unit 2810 located between the upper electrode2820 and the ground electrode 2830 and particles present in a seconddisplay unit 2815 located between the lower electrode 2825 and theground electrode 2830 can be controlled independently from each other.Thus, the display device 2800 can reflect light of different wavelengthsagainst both sides (i.e., the side of the upper electrode 2820 and theside of the lower electrode 2825), and accordingly can realize adisplay, both sides of which are controlled independently from eachother.

Hereinafter, a description will be given on a display method and deviceusing photonic crystal characteristics in accordance with anotherembodiment of the present invention, in which an electric field isapplied to the dispersion including particles having electric chargesand a solvent to control inter-particle distances to thereby reflectlight of a certain wavelength range.

Like the display device 900 in accordance with one embodiment of thepresent invention shown in FIG. 9, a display device (not shown) inaccordance with another embodiment of the present invention may includea display unit and an electric field generating and/or applying unit,and the display unit may include a plurality of particles havingelectric charges, dispersed in a certain solvent.

In accordance with another embodiment of the present invention, if anelectric field is applied to the particles, electrical attraction of apredetermined direction acts on the particles due to the electriccharges of the particles, and the particles are drawn to one side byelectrophoresis, thus narrowing the inter-particle distances. On thecontrary to this, as electrical repulsion acts between the particleshaving the electric charges of the same sign, the inter-particledistances do not become continuously narrower and reach a predeterminedequilibrium state. Therefore, the inter-particle distances can bedetermined depending on the relative strength of electrical attractioncaused by the electric field and the electrical attraction between theparticles having electric charges of the same sign, and thus theplurality of particles arranged at predetermined intervals can functionas photonic crystals. That is, because the wavelength of light reflectedfrom the plurality of regularly arranged particles is determined by thedistances between the particles, the wavelength of light reflected fromthe particles can be changed by controlling the distances between theparticles.

Meanwhile, it should be noted that the configurations and embodimentsdescribed above with reference to FIGS. 12 to 23 are also applicable tothe display device in accordance with another embodiment of the presentinvention.

The following is a description of a display method and device usingphotonic crystal characteristics in accordance with still anotherembodiment of the present invention, in which an electric field and/ormagnetic field is applied to the dispersion particles having electriccharges and magnetism or magnetic property and a solvent to controlinter-particle distances of the particles and thus reflect light of acertain wavelength range.

In accordance with still another embodiment of the present invention,there is provided a display device in which an electric field and/ormagnetic field is applied to the dispersion including the solvent andthe particles having electric charges and magnetism or magnetic propertyto control the inter-particle distance. The inter-particle distances ofthe particles having magnetism or magnetic property can be controlled bya magnetic field on the same principle as the inter-particle distancesof the particles having electric charges are controlled by an electricfield. Therefore, a detailed description of the operating principle willbe omitted. In accordance with still another embodiment of the presentinvention, the particles having electric charges and magnetism mayinclude a super-paramagnetic material or magnetic nano-particles, suchas iron (Fe) oxide, nickel (Ni) oxide, and cobalt (Co) oxide, inaddition to a material having electric charges. It should be noted,however, that the composition of the particles in accordance with stillanother embodiment of the present invention is not limited those listedabove but may be appropriately changed within the scope of the objectsof the present invention.

More specifically, in accordance with still another embodiment of thepresent invention, in a state where a display for displaying a specificcolor on the display unit is realized by applying a predeterminedelectric field to a display unit including particles having electriccharges and magnetism, if a magnetic field having a predetermineddirection and magnitude is applied to a partial region of the displayunit, the color displayed on the corresponding partial region of thedisplay unit can be changed. Additionally, in accordance with stillanother embodiment of the present invention, in a state where a displayfor displaying a specific color on a partial region of the display unitis realized by applying a magnetic field having a predetermineddirection and magnitude to the partial region of a display unitincluding particles having electric charges and magnetism, if anelectric field having a predetermined direction and magnitude is appliedto the entire region of the display unit, a display over the entire areaof the display unit may be reset. That is, with the display device inaccordance with still another embodiment of the present invention, theinter-particle distances can be controlled using a magnetic field, aswell as an electric field, and therefore a display control method can bediversified.

FIG. 29 is a view illustrating the configuration of a display device inaccordance with still another embodiment of the present invention.

Referring to FIG. 29, a display device 2900 in accordance with stillanother embodiment of the present invention may include a display unit2910 including particles 2912 having electric charges and magnetism,electric field generating and/or applying units 2922, 2924, and 2926 forapplying an electric field to the display unit 2910, and a magneticfield generating and/or applying unit 2930 for applying a magnetic fieldto the display unit 2910. The magnetic field applying unit 2930 mayinclude an electromagnet 2932 and a coil 2934 to control the intensityand direction of the magnetic field applied to the display unit 2910. Inaddition, the magnetic field applying unit 2930 may take the form of astimulus fixed and installed at a specific region of the display device2900, or may take the form of a pen so as to be manipulated by a user toapply a magnetic field to a given or desired region on the display unit2910.

Referring to FIG. 29, the particles 2912 located in between the firstelectrodes 2922 to which no voltage is applied may be irregularlyarranged, the particles 2912 located in between the second electrodes2924 to which a voltage is applied may be regularly arranged whilemaintaining predetermined inter-particle distances by the electric fieldapplied into between the second electrode 2924. The particles 2912affected by the magnetic field applied by the magnetic field generatingand/or applying unit 2930, as well as by the electric field applied bythe third electrode 2926, may be arranged more densely or more sparselyin a regular way than the particles 2912 located in between the secondelectrode 2924.

Continually, referring to FIG. 29, the magnetic field applying unit 2930may include an electromagnet 2932 having a coil 2934 wound therearoundto generate a magnetic field generated by induction current and a powersupply (not shown) for flowing current in the coil 2934. With thisconfiguration, since the intensity of the magnetic field induced fromthe coil 2934 and produced by the electromagnetic field 2932 can bevaried by adjusting a change in the current supplied to the coil 2934.Thus, the inter-particle distances of the particles contained in thedisplay unit 2910 can be controlled variously and finely, and, as aresult, a display for displaying a structural color over the fullwavelength range on the display unit 2910 can be realized.

Moreover, referring to FIG. 29, the magnetic field applying unit 2930 inaccordance with such a still another embodiment of the present inventioncan perform the “erase” function of resetting the display realized onthe display unit 2910, as well as the “write” function of realizing adisplay of various colors on the display unit 2910. That is, inaccordance with this still another embodiment of the present invention,by varying the intensity and direction of current flown to the coil 2934mounted on the magnetic field generating and/or applying unit 2930, theinter-particle distances of the particles contained in the display unit2910 may be set to specific distances, or, on the contrary, theinter-particle distances of the particles contained in the display unit2910 may be reset or initialized. Therefore, with the display device2900, it is possible to realize a color board having various backgroundcolors together with functions of writing and/or erasing of charactersin various colors on the background, as well as a display for displayinga structural color over the full wavelength range.

Meanwhile, it should be noted that the configurations and embodimentsdescribed above with reference to FIGS. 12 to 23 are also applicable tothe display device in accordance with still another embodiment of thepresent invention.

Experimental Results

First, FIGS. 30 and 31 are graphs and photographs showing lightreflected from the particles as a result of performing an experiment forthe application of an electric field when the particles having electriccharges are dispersed in a solvent having electrical polarizationcharacteristics in accordance with one embodiment of the presentinvention. For reference, in the experiment of FIGS. 30 and 31,particles having a size of 100 to 200 nm, charged with negative chargesand coated with a silicon oxide film were used as the particles havingelectric charges, a solvent having a polarity index greater than 1 wasused as the solvent having electrical polarization characteristics. Theintensity of a voltage applied to apply an electric field to thedispersion including the particles, and the solvent was set variously inthe range of 0 to 5 V. Meanwhile, the graphs shown in FIG. 30 depict thereflectance of light reflected from the particles in the wavelengthrange of the visible light spectrum when electric fields of variousintensities are applied. From FIG. 30, it can be seen that the greaterthe degree of change in the wavelength pattern of reflected light withchange in the intensity of an electric field, the larger the change inthe inter-particle distances. This means that light of more variouswavelengths can be reflected from the particles by controlling theintensity of the electric field.

Referring to FIG. 30, it can be seen that a wavelength pattern of lightreflected from particles depends on the intensity of an applied electricfield (i.e., intensity of a voltage). More specifically, it can be seenthat, the higher the intensity of an applied electric field (i.e.,intensity of a voltage), the shorter the wavelength of the lightreflected from the particles on the whole. According to the experimentresult of FIG. 30, it can be seen that the higher the intensity of anapplied electric field (i.e., intensity of a voltage), the more thecolor of the light reflected from the particles changes to blue fromred. Referring to FIG. 31, the aforementioned change in the color of thereflected light can be visually verified.

Next, FIGS. 32 and 33 are graphs showing the wavelength of lightreflected from the particles as a result of performing an experiment forthe application of an electric field when the particles having electriccharges are dispersed in various solvents having different polarityindices in accordance with one embodiment of the present invention. Forreference, in the experiment of FIGS. 32 and 33, particles having a sizeof 100 to 200 nm, charged with negative charges and coated with asilicon oxide film were used as the particles having electric charges,and solvents having polarity indices of 0, 2, 4, and 5 were used as thesolvent having electrical polarization characteristics. Morespecifically, the graphs (a), (b), (c), and (d) of FIG. 32 depictexperimental results for the solvents having polarity indices of 0, 2,4, and 5, respectively, and the graphs (a), (b), (c), and (d) of FIG. 33depict experimental results for a solvent obtained by mixing a solventhaving a polarity index of 0 and a solvent having a polarity index of 4at ratios of 90:10, 75:25, 50:50, and 0:100, respectively. Meanwhile,the graphs shown in FIGS. 32 and 33 depict the reflectance of the lightreflected from the particles in the wavelength range of a visible lightspectrum when electric fields of various intensities are applied. Thegreater the degree of change in the wavelength pattern of reflectedlight with change in the intensity of an electric field, the larger thechange in the inter-particle distances. This means that light of morevarious wavelengths can be reflected from the particles by controllingthe intensity of the electric field.

Referring to FIG. 32, from graph (a) showing the experimental result forthe solvent having a polarity index of 0, it can be seen that a changein the intensity of an electric field (i.e., intensity of a voltage)causes almost no change in the wavelength pattern of reflected lightbetween the different voltages. It can be seen that the higher thepolarity index (i.e., as the experimental results proceed toward graph(d) from graph (a)), the greater the change in the wavelength pattern ofreflected light with changes in the intensity of an electric field(i.e., intensity of a voltage). Further, referring to FIG. 33, it can beseen that, the higher the ratio of the solvent having a high polarityindex (i.e., as the experimental results proceed toward graph (d) fromgraph (a)), the greater the changes in the wavelength pattern ofreflected light with changes in the intensity of the electric field(i.e., intensity of a voltage).

From the experimental results discussed above, it can be seen that, withthe display device in accordance with one embodiment of the presentinvention, photonic crystals capable of reflecting light of a certainwavelength can be realized by properly adjusting the charge amountand/or polarization amount of the particles, the polarization amount ofthe solvent, and/or the intensity of an applied electric field, andaccordingly a display of a certain wavelength range (full spectrum) canbe realized.

Next, FIGS. 34 and 35 are graphs and photographs showing light reflectedfrom the particles as a result of performing an experiment for theapplication of an electric field when the particles having electriccharges and electrical polarization characteristics are dispersed in asolvent in accordance with one embodiment of the present invention. Forreference, in the experiment of FIGS. 34 and 35, SrTiO₃ particles (see(a) of FIG. 34) and BaTiO₃ particles (see (b) of FIG. 34), both of whichare charged with electric charges, were used as the particles havingelectric charges and electrical polarization characteristics, and theparticles were dispersed in a solvent having a polarity index of 0.

Referring to FIG. 34, it can be seen that the higher the intensity of anelectric field applied to the particles and the solvent, the lower thereflectance of light on the whole. From this experimental result, it canbe concluded that upon application of an electric field, the particlesdispersed in the solvent can be electrically polarized and arranged inthe direction of the electric field (see (b) of FIG. 35), and thisarrangement leads to a decrease in the number of particles capable ofreflecting incident light and reduces the reflectance of light. Althoughthis experiment does not involve a sharp change in the wavelength ofreflected light which will be produced using a configuration in which anelectric field is applied when particles having electrical polarizationcharacteristics are dispersed in a nonpolar solvent, it was found thatthe particles are arranged in a constant direction as the electric fieldis applied. From this, it can be concluded that the wavelength ofreflected light can be varied by optimizing the conditions, such aselectric charges on the particle surfaces.

Next, FIG. 36 is a view showing experimental results for theconfiguration for realizing a transparent display in accordance with oneembodiment of the present invention. For reference, in this experiment,particles, a solvent, and electrodes that are made of a transparentmaterial that transmits light in a visible spectrum were used, and thedegree of transparency of display was visually observed while graduallyincreasing the intensity of an electric field applied to the displaydevice using photonic crystals.

Referring to FIG. 36, if the intensity of an electric field isrelatively low, it can be seen that a predetermined color was displayedon the display device as light of a visible spectrum is reflected byphotonic crystals (see (a) and (b) of FIG. 36). However, if theintensity of an electric field is relatively high, it can be seen thatthe color displayed on the display device became noticeably lighter asthe wavelength range of light reflected by photonic crystals isgradually shifted from the visible spectrum to the ultraviolet spectrum(see (c) of FIG. 36). If the intensity of an electric field becomes muchhigher, it can be seen that the display device turns into a transparentstate while displaying no color as the wavelength range of lightreflected by photonic crystals is completely out of the visible spectrum(see (d) and (e) of FIG. 36). Using this characteristic, the displaydevice in accordance with the present invention may be utilized as smartglass, such as color changing glass.

FIG. 37 is a view showing a result of an experiment of the performanceof a display varying with the observation angle of the display device(i.e., an experimental result for the viewing angle of a display) inaccordance with one embodiment of the present invention.

Referring to FIG. 37, it can be seen that even if the observation angleof the display device in accordance with one embodiment of the presentinvention varies from 20° to 70°, almost no change was observed in thecolor patterns 3710 to 3760 of reflected light. It was found that, whilethe conventional photonic crystal display device has the disadvantage ofshowing a significant change in color pattern depending on theobservation angle, the display device in accordance with the presentinvention has the advantage of showing a constant color pattern withoutalmost any change in color pattern depending on the observation angle.It is understood that this advantage derives from the fact that thephotonic crystals formed by the display device in accordance with thepresent invention are quasi crystals having a short range order.Accordingly, the display device in accordance with the present inventioncan greatly improve display performance in comparison with theconventional display device which merely forms photonic crystals havinga long range order.

Meanwhile, FIGS. 38 and 39 are views showing results of actuallyrealizing a display by applying an electric field (FIG. 38) and amagnetic field (FIG. 39) to particles having electric charges andmagnetism in accordance with still another embodiment of the presentinvention. For reference, in this experiment, particles including ironoxide (Fe₃O₄; magnetite) and coated with silicon oxide (SiO_(X)) havingnegative charges were used as the particles, and these particles, whichare dispersed in a solvent, were injected into the display device.

First, in the experiment of FIG. 38, indium tin oxide, which is one oflight transmissive electrode materials, was used as the material of theelectrode for applying an electric field. In addition, in thisexperiment, particles having negative charges are arranged, biasedtoward the upper electrode, by applying a positive voltage to the upperelectrode of the display device. Meanwhile, in this experiment, voltagesof 0 V, 1 V, 2 V, . . . , 10 V were sequentially applied to theelectrode of the display device, and the color of light reflected fromthe display device upon application of the voltage of 0 to 10 V were asshown in (a) to (k) of FIG. 38, respectively.

Referring to FIG. 38, it can be seen that, while no particular colorchange was observed if a relatively low voltage of 0 to 4 V was applied,a distinct color change was observed if a relatively high voltage of 5to 10 V was applied. Particularly, the higher the applied voltage, themore the color observed in the display device changes to blue fromgreen. It would be considered that this is because the inter-particledistances become closer with an increase in the magnitude of theelectrical attraction (i.e., a force that causes electrophoresis) actingon the particles due to the electric field, and thus the wavelength oflight reflected from the particles becomes shorter (see (a) to (k) ofFIG. 38).

Next, in the experiment of FIG. 39, the intensity of a magnetic fieldapplied to the display device was gradually increased by graduallydecreasing the distance between a permanent magnet for generating amagnetic field and the display device.

Referring to FIG. 39, it can be seen that the wavelength of the lightreflected from the display device varies with a change in the intensityof a magnetic field. More specifically, it can be seen that the lowerthe intensity of a magnetic field, the longer the wavelength ofreflected light of red, and the higher the intensity of a magneticfield, the shorter the wavelength of reflected light of blue.

From the experimental results of FIGS. 38 and 39, the inter-particledistances can be changed independently by applying an electric fieldand/or magnetic field to the display device. Using this characteristic,it is possible to manufacture a unique display device which uses anelectric field to erase a display realized by a magnetic field, or, onthe contrary, uses a magnetic field to form a certain pattern on adisplay realized by an electric field.

As explained above, with the display device in accordance with thepresent invention, a structural color over the full wavelength range canbe realized by controlling the inter-particle distances of the particleshaving electric charges to thus control the wavelength of lightreflected from the particles. Moreover, with the display device inaccordance with the present invention, various and precise displays canbe realized by independently controlling the particles having electriccharges, and the effect of making the maintenance and repair of thedisplay device easier can be achieved. In particular, as compared withthe existing displays, such as an electronic ink, that can only displaya specific color and requires the use of a separate color filter todisplay a color different from the specific color, the efficiency of thedisplay device in accordance with the present invention lies in that itcan realize a display for effectively displaying a structural color overthe full wavelength range without the use of a separate color filter.

Although the above embodiments have been described focusing on thedisplay device using photonic crystal characteristics, the configurationof the present invention is applicable in various fields, includingcolor changing glass, color changing wallpapers, color changing solarcells, color changing sensors, color changing papers, color changingink, anti-counterfeit tags, and so on. For example, using this concept,it is possible to manufacture a portable biosensor capable of detectinga chemical reaction without expensive measurement equipment byconverting a chemical signal obtained from the chemical reaction into anelectric signal and displaying the electric signal in a certain color.Also, if a material whose phase can be changed by light, heat, pressure,etc. is used as the solvent used for the display device of the presentinvention, electronic paper, electronic ink, etc. that reflect a certaincolor in a stable and fixed manner can be realized. Moreover, byincorporating a material, such as a phosphor material or quantum dot(QD) material, in the particles or solvent contained in the displaydevice in accordance with the present invention, a display usingphotonic crystals may be realized in a bright environment, and a displayusing phosphor or quantum dots may be realized in a dark environment orultraviolet environment.

While the invention has been shown and described with respect to theparticular embodiments, it will be understood by those skilled in theart that various changes and modification may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A display method using photonic crystal characteristics, wherein aplurality of particles having electric charges with the same polarity asone another are dispersed in a solvent which is electrically polarizedwhen electric field is applied thereto and whose electrical polarizationamount changes as the applied field changes; wherein by applying theelectric field, inter-particle distances between the plurality ofparticles are controlled in a state when the solvent is electricallypolarized; and wherein the inter-particle distances between theplurality of particles change as at least one of intensity and directionof the field changes, so that wavelength of light reflected from theparticles changes according to the changes of the inter-particledistances.
 2. The method of claim 1, wherein as the electric field isapplied, first electrical force is generated between the appliedelectrical field and the charged particles to cause electrophoresis ofthe particles, second electrical force is generated between theparticles charged with the same polarity as one another, and thirdelectrical force is generated from the electrical polarization of thesolvent; and wherein the first to third electrical forces interact witheach other so that the inter-particle distance of the particles ismaintained within a specific range, and, thus, light with a specificwavelength range is reflected from the particles.
 3. The method of claim1, wherein the solvent includes superparaelectric or ferroelectricmaterial.
 4. The display method of claim 1, wherein a difference inrefractive index between the particles and the solvent is more than orequal to 0.3.
 5. The display method of claim 1, wherein the solventincludes a material having a polarity index of 1 or greater.
 6. Thedisplay method of claim 1, wherein the particles and the solvent areencapsulated with a capsule made of light transmitting material.
 7. Thedisplay method of claim 1, wherein the particles and the solvent arepartitioned with a wall made of insulating material.
 8. The displaymethod of claim 1, wherein the particles and the solvent are dispersedin a droplet form in light transmitting medium.
 9. The display method ofclaim 1, wherein a region to which the electric field is applied isdivided into at least two partial regions; and wherein the electricfield is respectively applied to each of the divided partial regions.10. The display method of claim 1, wherein, after applying the electricfield, an electric field having the opposite direction to the appliedelectric field is applied to reset the inter-particle distances.
 11. Thedisplay method of claim 1, wherein, before applying the electric filed,a standby electric field is applied in order to maintain theinter-particle distance at predetermined inter-particle distances. 12.The display method of claim 1, wherein the inter-particle distances varywith changes in at least one of application duration and applicationperiod of the electric field.
 13. The display method of claim 1, whereinan electric energy is generated using light passing through, theparticles, and the electric field is applied using the electric energy.14. The display method of claim 1, wherein, by applying the electricfield through an upper electrode and a lower electrode, and by settingthe intensity of the electric field to be less than a predeterminedvalue to control the moving range of the particles to be less than apredetermined value, a unique color of one of the particles, thesolvent, the upper and lower electrodes is displayed.
 15. The displaymethod of claim 1, wherein, by applying the electric field through anupper electrode and a lower electrode, and by setting the intensity ofthe electric field to be greater than or equal to a predetermined valueto move the particles toward at least partial region of either the upperelectrode or the lower electrode, a unique color of one of theparticles, the solvent, the upper and lower electrodes is displayed. 16.The display method of claim 1, wherein by applying an electric field ina state where second particles with opposite polarity to the pluralityof the particle are further dispersed in the solvent, the inter-particledistances between the particles and the inter-particle distances betweenthe second particles are controlled differently from each other by theelectric field.
 17. A display method using photonic crystalcharacteristics, wherein a plurality of particles having electriccharges with the same polarity as one another are dispersed in asolvent, the particles being electrically polarized when electric fieldis applied thereto, and electrical polarization amount of the particleschanges as the applied field changes; wherein by applying the electricfield, inter-particle distances between the plurality of particles arecontrolled in a state when the particles are electrically polarized; andwherein the inter-particle distances between the plurality of particleschange as at least one of intensity and direction of the field changes,so that wavelength of light reflected from the particles changesaccording to the changes of the inter-particle distances.
 18. The methodof claim 17, wherein as the electric field is applied, first electricalforce is generated between the applied electrical field and the chargedparticles to cause electrophoresis of the particles, second electricalforce is generated between the particles charged with the same polarityas one another, and third electrical force is generated from theelectrical polarization of the particles; and wherein the first to thirdelectrical forces interact with each other so that the inter-particledistance of the particles is maintained within a specific range, and,thus, light with a specific wavelength range is reflected from theparticles.
 19. The method of claim 17, wherein the particles includesuperparaelectric or ferroelectric material.
 20. The display method ofclaim 17, wherein a difference in refractive index between the particlesand the solvent is more than or equal to 0.3.
 21. The display method ofclaim 17, wherein the particles and the solvent are encapsulated with acapsule made of light transmitting material.
 22. The display method ofclaim 17, wherein the particles and the solvent are partitioned with awall made of insulating material.
 23. The display method of claim 17,wherein the particles and the solvent are dispersed in a droplet form inlight transmitting medium.
 24. The display method of claim 17, wherein aregion to which the electric field is applied is divided into at leasttwo partial regions; and wherein the electric field is respectivelyapplied to each of the divided partial regions.
 25. The display methodof claim 17, wherein, after applying the electric field, an electricfield having the opposite direction to the applied electric field isapplied to reset the inter-particle distances.
 26. The display method ofclaim 17, wherein, before applying the electric filed, a standbyelectric field is applied in order to maintain the inter-particledistance at predetermined inter-particle distances.
 27. The displaymethod of claim 17, wherein the inter-particle distances vary withchanges in at least one of application duration and application periodof the electric field.
 28. The display method of claim 17, wherein anelectric energy is generated using light passing through the particles,and the electric field is applied using the electric energy.
 29. Thedisplay method of claim 17, wherein, by applying the electric fieldthrough an upper electrode and a lower electrode, and by setting theintensity of the electric field to be less than a predetermined value tocontrol the moving range of the particles to be less than apredetermined value, a unique color of one of the particles, thesolvent, the upper and lower electrodes is displayed.
 30. The displaymethod of claim 17, wherein, by applying the electric field through anupper electrode and a lower electrode, and by setting the intensity ofthe electric field to be greater than or equal to a predetermined valueto move the particles toward at least partial region of either the upperelectrode or the lower electrode, a unique color of one of theparticles, the solvent, the upper and lower electrodes is displayed. 31.The display method of claim 17, wherein by applying an electric field ina state where second particles with opposite polarity to the pluralityof the particle are further dispersed in the solvent, the inter-particledistances between the particles and the inter-particle distances betweenthe second particles are controlled differently from each other by theelectric field.
 32. A display device using photonic crystalcharacteristics, comprising: a display unit in which a plurality ofparticles having electric charges with the same polarity as one anotherare dispersed in a solvent which is electrically polarized when electricfield is applied thereto and whose electrical polarization amountchanges as the applied field changes; and an electric field generatingand/or applying unit for generating an electric field applied to thedisplay unit, wherein, by applying the electric field to the displayunit, inter-particle distances between the plurality of particles arecontrolled in a state when the solvent is electrically polarized; andwherein the inter-particle distances between the plurality of particleschange as at least one of intensity and direction of the field changes,so that wavelength of light reflected from the particles changesaccording to the changes of the inter-particle distances.
 33. Thedisplay device of claim 32, wherein the particles and the solvent areencapsulated with a capsule made of light transmitting material.
 34. Thedisplay device of claim 32, wherein the particles and the solvent arepartitioned with a wall made of insulating material.
 35. The displaydevice of claim 32, wherein a region to which the electric field isapplied is divided into at least two partial regions; and wherein theelectric field is respectively applied to each of the divided partialregions.
 36. The display device of claim 32, further comprising a solarcell for generating an electric energy using light passing through theparticles, wherein the electric field is applied using the electricenergy.
 37. The display device of claim 32, wherein, by applying theelectric field through an upper electrode and a lower electrode, and bysetting the intensity of the electric field to be greater than or equalto a predetermined value to move the particles toward at least partialregion of either the upper electrode or the lower electrode, a uniquecolor of one of the particles, the solvent, the upper and lowerelectrodes is displayed.
 38. A display device using photonic crystalcharacteristics, comprising: a display unit in which a plurality ofparticles having electric charges with the same polarity as one anotherand having electrical polarization characteristics are dispersed in asolvent, the particles being electrically polarized when electric fieldis applied thereto, and electrical polarization amount of the particleschanges as the applied field changes; an electric field generatingand/or applying unit for generating an electric field applied to thedisplay unit, wherein, by applying the electric field to the displayunit, inter-particle distances between the plurality of particles arecontrolled in a state when the particles are electrically polarized; andwherein the inter-particle distances between the plurality of particleschange as at least one of intensity and direction of the field changes,so that wavelength of light reflected from the particles changesaccording to the changes of the inter-particle distances.
 39. Thedisplay device of claim 38, wherein the particles and the solvent areencapsulated with a capsule made of light transmitting material.
 40. Thedisplay device of claim 38, wherein the particles and the solvent arepartitioned with a wall made of insulating material.
 41. The displaydevice of claim 38, wherein a region to which the electric field isapplied is divided into at least two partial regions; and wherein theelectric field is respectively applied to each of the divided partialregions.
 42. The display device of claim 38, further comprising a solarcell for generating an electric energy using light passing through theparticles, wherein the electric field is applied using the electricenergy.
 43. The display device of claim 38, wherein, by applying theelectric field through an upper electrode and a lower electrode, and bysetting the intensity of the electric field to be greater than or equalto a predetermined value to move the particles toward at least partialregion of either the upper electrode or the lower electrode, a uniquecolor of one of the particles, the solvent, the upper and lowerelectrodes is displayed.